An electronic device and a power supply method thereof are provided. The electronic device includes a control circuit, a detachable power supply device, and an auxiliary power supply device. The control circuit is coupled to a power supply terminal coupled to a system load. When the detachable power supply device is assembled to the electronic device, the detachable power supply device is coupled to the control circuit and supplies power to the system load. The auxiliary power supply device is coupled to the control circuit. When the electronic device is not turned on and the detachable power supply is removed from the electronic device, the electronic device is not turned on by the auxiliary power supply device. When the electronic device is turned on and the detachable power supply is removed from the electronic device, power is continuously supplied to the system load by the auxiliary power supply device.